1. Field of the Invention
The present invention relates to image read control of a facsimile apparatus.
2. Related Background Art
In a prior art facsimile apparatus, read image data is transmitted in the following manner. As shown in FIG. 2, a plurality of line buffers each capable of storing one line of raw data (non-coded data) are provided and data read by a CCD is binarized and transferred to the line buffers. When one line of data is stored in the line buffer, it is transferred to an encoder, encoded thereby and stored in an image buffer. The data stored in the image buffer is sequentially read and sent to a modem.
In the prior art read control, a line sync signal determined by a storage time of the CCD is used as a reference, and if the line buffer is vacant (or free) when the line sync signal is applied, an image is read and a document sheet is fed, and if the line buffer is full, the reading is not carried out but it waits until the line buffer becomes vacant.
Accordingly, the operation of the read system depends on the complexity of the document sheet image and a communication rate. For a simple image, a data compression rate is high and the image can be transmitted at a high rate and it is rare that the line buffer becomes full. Thus, the image can be continuously read at a substantially constant speed. For a complex image, the data compression rate is low and a transmission bit rate cannot follow a generation speed of one line of encoded data. Thus, the image buffer becomes full and the line buffer becomes full and the operation is intermittent. In a worst case, the intermittent operation is such that each time one line is read, the vacant state of the line buffer is waited before the next line is read.
FIG. 3 shows the movement of a document sheet feed roller when a drive trigger is outputted to a document sheet feed stepping motor. As stated above, the read operation depends on the document sheet. Even if the drive trigger is outputted to the document sheet feed stepping motor as shown in FIG. 3, there is a delay before the document sheet feed roller is actually moved. Further, since the read operation of the image and the output of the drive trigger are synchronized, if a plurality of lines are to be continuously read, the first line and the second line read substantially same area. FIG. 4 shows the movement of the document sheet feed roller in the intermittent reading by every other line. Since there is still a delay to the drive trigger before the feed roller is actually moved, the document sheet feed roller is rotated by two lines after it has read the substantially same area in the first line and the second line. Thus, when the intermittent reading by a small number of lines is effected, the linear image reading is not attained and the image disturbed.